Currently, the main chemical compounds in industry are synthesized from petroleum resources. However, petroleum resources are limited and the combustion of petroleum products produces CO2, a primary greenhouse gas. As an alternative to fossil fuel, increased interest in the biomass energy has developed. The biomass utilization could lead to the prevention of global warming because its combustion does not lead to an increase in CO2 gas in the atmosphere. For example, the use of bioethanol, obtained from biomass/sugarcane, in gasoline blending has had positive effects such as reduction in vehicle emissions of gases like CO, CH4, reduction in green house gases (CO2), reduction of the dependence on petroleum products and imports of crude oil. Moreover, bioethanol replaces gasoline additives like MTBE and lead which are sources of surface and ground water contamination and dangerous to human health. However, bioethanol blending also has some negative effects such as increased emissions of aldehyde, known to be a human carcinogen, increased emissions of NOx, evaporative emissions and fuel consumption. There is concern for health as E10 (in India the gasoline blend contains 10% ethanol) vapor emissions will be greater than those from regular gasoline. Hence, it is preferable to convert bioethanol into aromatics and olefins which can be blended with gasoline or utilized for petrochemical production. One of the essential raw materials in the petrochemical industry is propylene, which is widely produced as a co-product of ethylene, by steam and thermal cracking of naphtha. However, this process is not optimal for the production of propylene. Thus, the development of propylene production processes from biomass resources such as bioethanol is highly desirable.
Aromatics are one of the basic raw materials in the chemical industry. Benzene (B), toluene (T) and xylenes (X), collectively known as BTX, are the most widely used aromatic hydrocarbons. The basic commercial processes for aromatic hydrocarbons production are solid-fuel process, pyrolysis and catalytic reforming, using crude oil. Now over 80% of aromatic hydrocarbons are produced by pyrolysis of tars and catalytic reforming, of which the feedstock is derived from crude oil. As an alternative to the use of crude oil, the catalytic aromatization of alcohols and ethers has generated a great deal of interest for the production of aromatic hydrocarbons. Catalytic conversions of methanol or diethyl ether (DEE) to gasoline (MTG) and light olefins (MTO) have been extensively studied. While new catalysts are being developed, known catalysts have been investigated for the production of aromatic hydrocarbons.
U.S. Pat. No. 4,698,452 describes the formation of ethylene from aqueous ethanol on mesopores ZSM-5 catalyst having Zn and Mn metals. However, these catalysts are not effective for the formation of aromatics/gasoline range products.
U.S. Pat. No. 4,621,164 describes the production of gaseous hydrocarbons from aqueous ethanol with various concentrations of water in presence of bifunctional ZSM-5 catalyst. However, the process is not aimed at producing material suitable for effective formation of aromatics.
U.S. Pat. No. 4,873,392 describes the production of ethylene from diluted ethanol on ZSM-5 bearing triflic acid and La metal at various reaction temperatures. However, this patent does not disclose the production of aromatics/gasoline range products.
U.S. Pat. No. 6,323,383 describes the formation of variety of chemicals such as ethylene, acetaldehyde, di-ethyl ether, 1-butanol and 1,3-butadiene from ethanol, over Ca, Cu, Fe loaded ZSM-5 catalyst. But, this process is not aimed at producing material suitable for aromatics production.
WO application 2009/098269 describes the dehydration of ethanol into ethylene and propylene with a pentasil zeolite based catalyst under various reaction conditions. However, this process does not describe the production of aromatics/gasoline range hydrocarbons.
US application 2006/0149109 describes the dehydration of ethanol and methanol into ethylene on a molecular sieve (SAPO) under various reaction conditions. However, this process does not describe the production of aromatics/gasoline range hydrocarbons.
US applications US 2011/0107662A1 and US 2011/0124927A1 describe a process for the conversion of ethanol first into syngas, followed by its conversion to one or more of methanol, ethanol, mixed alcohols and dimethyl-ethers, and eventually to gasoline in the final step. However, this process involves many intermediate compounds and multi reactor operations that limit the selectivity and yields of the gasoline.
U.S. Pat. No. 5,545,791 describes the conversion of lower aliphatic alcohol such as methanol to gasoline range hydrocarbons (mentioned as C5+ hydrocarbons) over Ti, Ni, Cu, Zn, Ag loaded ZSM-5 catalyst. But the process does not describe the composition of gasoline product with details such as aromatics, iso-paraffins, paraffins and naphthenes, which is indeed necessary to address the present fuel specifications to understand its quality and suitability for gasoline applications.
US application 2010/0174127 describes the conversion of diluted ethanol into LPG and gasoline over ZSM-5 catalyst which does not possess mesoporosity and nano crystal size. Moreover, the process operates at very low Weight Hourly Space Velocity (WHSV) (0.03 to 0.80) and under severe conditions that generally cause the rapid deactivation of the catalyst by coke deposition.
EP publication 0340061 and U.S. Pat. No. 4,847,223 describe the conversion of diluted aqueous ethanol into ethylene, over triflic acid incorporated onto ZSM-5 catalyst. However the process does not describe the formation of aromatics and LPG from ethanol.
WO application 2007/083241 describes the conversion of dilute ethanol into propylene and ethylene over solid acid catalyst in combination with various metal components such as Pb, Ca, Zn, Ag, Na, In, Ga and Ta. This process does not describe the formation of aromatics/gasoline range hydrocarbons.
The applications and patents described above focus on the formation of light olefins from aqueous ethanol. However, there remains a need for novel processes for the conversion of ethanol into high octane gasoline with LPG and olefins as valuable by-products.